Prior to laparoscopic or arthroscopic surgery, a cannula is inserted through the skin to access a body cavity through the cannula tube. In order to penetrate the skin, the distal end of the cannula tube is placed against the skin and a trocar is inserted through the tube. By pressing against the proximal end of the trocar, the point of the trocar is forced through the skin until it enters the body cavity. At this time, the cannula tube in inserted through the perforation made by the trocar and the trocar is withdrawn, leaving the cannula tube as an access way into the body cavity.
It has been found that often a great deal of force is required to cause the trocar point to penetrate the skin and underlying tissue. When the point finally breaks through this tissue, resistance to penetration is suddenly removed, and the trocar point can suddenly penetrate to reach internal organs of the body, which may cause lacerations and other injury to the internal organs.
For this reason, when a laparoscopy is performed, a pneumoperitoneum is first performed by introducing into the peritoneal cavity 3-4 liters of CO.sub.2. The pneumoperitoneum causes rising of the front abdominal wall and separation of the internal organs thereof and in particular, if the patient is placed into a slight Trendelemburg's position, the internal organs tend to move to the upper abdominal region. The trocar needle must then be introduced at an angle of 45.degree. in the lower periumbilical seat after sectioning of the skin (in a semi-circle around the lower edge of the navel) and the subcutis until reaching the aponeurosis. In addition, the trocar must be pushed carefully to avoid sudden deep penetration which could injure the internal organs or large vessels. However, despite all of these precautions, it is not always possible to avoid traumatic complications of the anatomic structures mentioned above and the complications connected with the pneumoperitoneum.
An additional problem in current laparoscopic procedures is that the thickness of abdominal tissue which must be traversed by the cannula tube varies from patient to patient. Because of this, a variety of different length cannulas are available for use in laparoscopic procedures, requiring the doctor to estimate the thickness of the abdominal tissue for the particular patient and then select a cannula having the proper length. Additionally, the present fixed length cannulas also contain no means for stabilizing the cannula against the surface of the patient's body. The result is that movement of the cannula during the laparoscopic procedure can cause tissue trauma in the area of skin surrounding the cannula. The surgeon performing the laparoscopic procedure must therefore stabilize the top of the cannula tube with one hand while using the other hand to insert the laparoscopic instrument into the cannula tube. Finally, present cannula tubes protrude from the skin's surface a substantial distance, which contributes to their general instability, easily becoming entangled in tubes and other devices used in the surgical procedure.
There is therefore a need in the prior art for a cannula tube which may be used to penetrate varying thicknesses of abdominal tissue, which provides a stable interface between the cannula and the patient and which exhibits a low profile above the surface of the patient's skin. Additionally, there is a need in the prior art for a trocar which will minimize the chance of accidental trauma to the abdominal organs due to penetration of the trocar to too great a depth within the abdominal cavity. The present invention is directed toward meeting these needs.